The invention relates to a method for reducing the operating temperature of a control device of a motor vehicle, especially of an automatic transmission, and to a transmission control having an electronic unit with,an electronic module and a hydraulic unit wherein the control device is situated in a transmission housing partly filled with oil and at least partly surrounded by oil.
It is known practice to place a control device for an automatic transmission outside the transmission housing and to connect control elements such as actuators via pipes situated in the transmission housing with the control device via pipes.
In DE 197 10 913 A1 discloses a transmission control especially for an automatic transmission in which the electrohydraulic control device and the electronic control device are placed together in a control housing in or directly on the transmission housing. For cooling the electronic control device to an acceptable temperature, there is provided a special cooling pipe plate with cooling pipes which are spatially disposed between the electrohydraulic and the electronic control devices. Transmission oil or engine cooling water flows through the cooling pipes which preferably lie in the cooler reflux.
However, this solution is disadvantageous because a long run of cables between the control means and the control device is required and additional space is needed for the control device placed outside the transmission housing.
In U.S. Pat. No. 4,271,728 and in EP 0 697 080, a solution is proposed which solves the problem of an additional space requirement due to the control unit being disposed in the oil sump of a transmission, the electric connections between the control electronics and the control means being designed as rigid wires according to EP 0 697 080.
In this known solution for cooling heat-producing electronics it s provided that heat is transferred via cooling fins to the transmission oil of the oil sump that surrounds the control electronics.
However, the cooling of the control electronics by merely surrounding the same with transmission oil proves problematic in operating situations with transmission oil at high temperatures. Especially in modern automatic transmissions the oil can reach temperatures of more than 100xc2x0 C. In such operating situations, the transmission oil can no longer absorb the amount of heat generated by the electronic components of the control electronics resulting in overheating of the electronic components Interruptions in the transmission control or complete failure of the control electronics also result.
Therefore; the problem to be solved by this invention is to make available a method for adjusting the operating temperature of a control device of a motor vehicle transmission and a transmission control wherein the control device is situated in the transmission housing surrounded by oil and the electronic modules of the control device are reliably protected against overheating.
The inventive method for targeted cooling of the electronic unit of a control device and the inventive development of the transmission control makes it possible to use the advantages of disposing the control device in the oil sump of the transmission with corresponding need of small space and short connections to the actuators.
The inventive solution further ensures that the power losses of the electronic modules are reliably removed and that the operating temperature is always kept low to prevent an interruption due to local overheating on an electroplate.
Thereby is not only the reliability of the transmission control increased but the service life of the electronic components is also extended.